under HPS lamps ( Table 1 ). High-pressure sodium lamps are rated to be 25% to 30% efficient at converting electrical energy to light; the other 70% to 75% is radiated as heat energy ( Spaargaren, 2001 ). Celosia is the only species considered cold
supplemental photosynthetic light to sustain steady supplies of high-quality produce during the off-season. Most greenhouse growers who use supplemental lighting rely on overhead high-pressure sodium lamps because of their capability to deliver adequate
flowering of Celosia, Impatiens, Salvia, Tagetes , and Viola HortScience 40 1336 1339 Randall, W.C. Lopez, R.G. 2014 Comparisons of supplemental lighting from high-pressure sodium lamps and light-emitting diodes during bedding plant seedling production
Injecting CO2 gas into mist water (CO2 mist) promoted rooting of Ilex aquifolium L. ‘Silver Variegated Standard’ stem cuttings in spring propagation while inhibiting rooting in the fall. Supplementary lighting from high pressure sodium lamps (HPS) for 16 hr daily had similar effects as CO2 mist in the spring and inhibited root growth in fall propagation. There was a positive interaction between CO2 mist and HPS in spring propagation, suggesting that the promotive effects of these variables were due to enhanced photosynthesis.
. 43 421 431 Cosgrove, D.J. 1981 Rapid suppression of growth by blue light Plant Physiol. 67 584 590 Currey, C.J. Lopez, R.G. 2013 Cuttings of Impatiens, Pelargonium , and Petunia propagated under light-emitting diodes and high-pressure sodium lamps
overhead SL ( Oh et al., 2010 ; Randall and Lopez, 2014 ; Sherrard, 2003 ). High-intensity discharge lamps, such as HPS and metal halide lamps, have traditionally been used for SL to increase greenhouse DLI. High-pressure sodium lamps have long been the
Four freesia cultivars were exposed to 24 hour·day-1 high-pressure sodium (HPS) lighting during various stages of their development. Upon emergence, freesia plants were exposed to the following four lighting treatments: 1) ambient; 2) ambient until shoot length was 5 to 8 cm followed by HPS lighting until flowering; 3) HPS lighting until shoot length was 5 to 8 cm followed by ambient lighting; and 4) continuous HPS lighting. Supplemental HPS lighting was provided at 37 μmol·m-2·s-1 at plant level in a glasshouse. Continuous lighting or lighting during flower development hastened flowering but reduced the number of flowering stems per corm, as well as stem length and weight. Lighting during the vegetative and flower initiation periods produced minor effects. The main benefit of supplemental lighting was found in total corm weight.
High-pressure sodium (HPS) lamps were as effective as incandescent (INC) lamps for controlling photoperiod with 10 cultivars of Chrysanthemum × morifolium Ramat. for up to 8 weeks when used at illuminances (108 to 215 lux) generally recommended. Two garden cultivars studied initiated flowering under long days (LD) with both lamps. In a second study, 11 chrysanthemum cultivars were grown under continuous irradiation from HPS lamps. Six cultivars were vegetative after 8 weeks; the other 5 cultivars developed crown buds or lost apical dominance.
Supplemental high-pressure sodium (HPS) irradiation of greenhouse-grown snapdragons (Antirrhinum majus L.) at a quantum flux density (QFD) of 105 ± 15 μE m−2s−1 reduced winter flowering time and increased fresh weight and stem length. Flowering time, fresh weight, and stem length were equal when plants were grown at both summer (8 × 10 cm) and winter (10 × 13 cm) spacings under HPS lamps, thereby increasing winter production/m2 by 63%. Reductions in flowering time and increases in fresh weight and stem length for cultivars grown under HPS lamps during the spring were smaller than for plants grown under HPS lamps during the winter. Differences in cultivar response were found in both studies.
Electronic dimming of high intensity discharge lamps offers control of photosynthetic photon flux (PPF) but is often characterized as causing significant spectral changes. Growth chambers with 400 W metal halide (MH) and high pressure sodium (HPS) lamps were equipped with a dimmer system using silicon controlled rectifiers (SCR) as high speed switches. Phase control operation turned the line power off for some period of the AC cycle. At full power the electrical input to HPS and MH lamps was 480 W (RMS) and could be decreased to 267 W and 428 W, respectively, before the arc was extinguished. Concomitant with this decrease in input power, PPF decreased by 60% in HPS and 50% in MH. The HPS lamp has characteristic spectral peaks at 589 and 595 nm. As power to the HPS lamps was decreased the 589 nm peak remained constant while the 595 nm peak decreased, equalling the 589 nm peak at 345 W input, and was almost absent at 270 W input. The MH lamp has a broader spectral output but also has a peak at 589 nm and another, smaller peak, at 545 nm. As input power to the MH lamps decreased the 589 nm peak diminished to equal the 545 nm peak. As input power approached 428 W the 589 nm peak shifted to 570 nm. While a spectral change was observed as input power was decreased in both MH and HPS lamps, the phytochrome equilibrium ratio (Pfr/Ptot) remain unchanged for both lamp types.